1. Field of the Invention
The present invention relates to a photoelectric conversion apparatus, and more specifically relates to an arrangement of an AD converter that converts analog signals obtained by means of photoelectric conversion to digital signals.
2. Description of the Related Art
Currently, MOS-type photoelectric conversion apparatuses are used for photoelectric conversion apparatuses employed in digital cameras and digital video recorders and the like. An MOS-type photoelectric conversion apparatus has many advantages compared to a CCD or the like, because circuits, such as a circuit for controlling the reading of signals from pixels and a circuit for processing output signals, can be formed in the same processes. In recent years, there arises a need for further increasing the speed of signal output in MOS-type photoelectric conversion apparatuses, and as one of the techniques for meeting that need, a construction having a plurality of AD converters each provided for each of a plurality of pixels, has been considered. For example, an AD converter can be provided for each of the pixel columns in the construction where pixels are arranged in a matrix such that analog data can be converted to digital data by column, thereby increasing the speed.
As one of such constructions, Japanese Patent Application Laid-Open No. 2005-136540 discloses a photoelectric conversion apparatus having a recursive AD converter provided for each column. This apparatus has a photoelectric conversion region with a plurality of pixels arranged therein, and a plurality of AD converters, arranged on the same semiconductor substrate.
The recursive AD converter disclosed in Japanese Patent Application Laid-Open No. 2005-136540 repeats comparison with a reference signal and amplification via an arithmetic amplifying circuit and a DA conversion circuit to calculate the result, starting from a higher order bit. Such recursive AD converter requires a path for feeding a signal obtained by decoding an output from a comparator back to a DA converter.
Conventionally, no sufficient consideration has been made for the relationship between this feedback path and the arrangement of elements constituting an AD converter. The present inventors' study has revealed that where the elements are arranged following the flow of a signal in the AD converter, the arrangement pitch of the elements constituting the AD converter may determine the arrangement pitch per pixel column.
In view of such technical problems, an object of the present invention is to provide a configuration that, when an AD converter is provided for each of pixel columns or each plurality of pixel columns, enables the elements to be arranged without increasing the element arrangement pitch for the pixel columns.